Performance of Circuit Switched Fall Back & Single Radio Voice Call Continuity from TD-LTE to UMTS

Voice call continuity between radio access technologies has been a requirement for many operators with the introduction of LTE networks. In this paper we investigated Circuit Switched Fall Back (CSFB) to UMTS-HSPA from TD-LTE network and SRVCC from TD-LTE to UMTS-HSPA test network. We analyzed the CSFB-to-UMTS performance both in Idle and connected modes for mobile originated and mobile terminated calls. The tests were conducted with and without packet switched handover (PSHO) feature to show the benefit of PSHO. The CSFB performance tests evaluated the CSFB call-setup times against the average 3G call setup delay. The tests showed that the CSFB set up times are quite significant compared to the normal circuit switched call setups in 3G networks. SRVCC handover measurements fulfilled the performance target of less than 0.3 seconds as required by 3GPP standards. The CSFB setup and SRVCC handover had a 100% success rate. In connected mode, the data application running in serving LTE cell continued on the target 3G NodeB cell with little interruption and didn't degrade quality of user experience.